The xylem is the vascular tissue responsible for the upward conduction of water and nutrients from the roots. The xylem tissue moves water and nutrients to various parts of the plant such as shoots and leaves. Its major components include xylem parenchyma, xylem fibers, tracheids, and xylem vessels.
The xylem parenchyma is comprised of parenchyma cells. Parenchyma cells are the only living cells in the xylem. They have thin cell walls, large vacuoles, prominent nucleus, and protoplasts. They have differing shapes although they are usually cylindrical and lobed in form. In the trunks of woody plants, the xylem parenchyma cells are colourless and are believed to be involved chiefly in storing starch, oils, and other ergastic substances. The inclusions in xylem parenchyma cells may contain tanninferous compounds. The wood, especially of flowering trees, has two major types of parenchyma cells: axial (i.e. parenchyma cells arranged around an axis) and radial (i.e. parenchyma cells arranged like rays of a circle, diverging in lines from a common center). Some axial and radial parenchyma cells though may form secondary thickenings at their cell walls. Parenchyma cells that develop secondary cell walls are referred to as sclerenchyma cells.